two brains?

http://www.newscientist.com/article/mg19926651.600-brains-apart-the-real-difference-between-the-sexes.html
"Brains Apart: The Real Difference between the Sexes"
by Hannah Hoag
July 16, 2008
NewScientist

"For the most part, the basic architecture of the brain, and its fundamental workings, were thought to be the same for both sexes.
Increasingly, though, those assumptions are being challenged. Research is revealing that male and female brains are built from markedly different genetic blueprints, which create numerous anatomical differences. There are also differences in the circuitry that wires them up and the chemicals that transmit messages between neurons. All this is pointing towards the conclusion that there is not just one kind of human brain, but two."

Here's a question: why stop at two? Are there other ways of dividing up people so as to reveal interesting differences between their brains? (Obviously, the answer is yes: just look at autistics). The question is: how far down do we want to go? How many subdivisions shall we make? (I think it is a practical question: what are our purposes?)

(this post is another post about seeing individuals rather than groups)